Thermal packs are well known in the prior art. Generally speaking, there are two primary types of thermal or hot and cold packs.
There is the so-called instant pack wherein separated ingredients are combined and chemically react to liberate or absorb heat and thus produce heating or cooling.
There is also the type of thermal pack commonly referred to as the gel pack. Gel packs essentially comprise an outer flexible package containing a gel which is cooled by placing it in a freezer or the like. Gel packs have the advantage over most instant packs of being flexible or moldable even when frozen. However, conventional gel packs do not readily lend themselves to use with the types of chemicals employed in instant packs to liberate or absorb heat. Thus, for many years, the consumer was faced with the choice of purchasing and using either an instant pack or a gel pack, both of which had certain drawbacks and disadvantages.
U.S. Pat. No. 3,804,077 discloses an instant hot or cold pack which also forms a gel. Included in the pack is a first sealed compartment containing particles of a first material such as calcium chloride or ammonium nitrate (depending upon whether an exothermic or endothermic reaction is desired) and starch particles.
When the first material and starch are mixed with water dispensed from a ruptured second compartment of the pack, a gel is immediately formed. This immediate formation of the gel impedes movement of the materials in the pack. This is a drawback since restriction of movement of the materials slows the rate at which chemical reaction occurs and reduces both the rate and range of temperature change. Temperature of the pack can vary widely over the extent thereof. Use of starch, it is believed, also results in the pack becoming hard and inflexible when frozen.
U.S. Pat. No. 4,462,224 discloses a thermal pack which is said to overcome the disadvantages of the prior packs by combining the advantages of an instant hot or cold pack with the advantages of a reusable cold pack.
U.S. Pat. No. 4,462,224 discloses a three-compartment, instant, reusable cold pack for removing heat from an object. A first compartment contains a predetermined amount of solvent comprised primarily of water. A second compartment contains a predetermined amount of a particulate chemical solute capable of essentially completely dissolving in the solvent and reacting therewith whereby a predetermined amount of heat is absorbed. A third compartment contains a predetermined amount of gelling agent capable of gelling with the solvent and solute solution after the cold of the pack has disappeared and the pack reaches ambient temperature.
Mixing of the contents of the first compartment and the second compartment produces an instant cooling effect in the manner of a conventional instant cold pack. Once the solution has returned to ambient temperature, the contents of the third compartment are joined with the contents of the first and second compartments and manually kneaded and mixed to produce a gel that allegedly will remain flexible when cooled to temperatures typically attainable in a freezer.
The pack of U.S. Pat. No. 4,462,224 has a number of disadvantages. The package itself is relatively complex in that it incorporates three compartments. If the proper sequence of mixing is not followed the pack can be rendered useless. If the second and third compartment contents are mixed by mistake prior to mixing of the first and second compartment contents, the cooling and gelling functions either do not occur or occur on a limited basis or in an ineffectual manner.
The same holds true if all three compartment contents are mixed at the same time. The gel material impedes relative movement of the other chemicals in the pack, slowing down the rate of chemical reaction and thus reducing the ultimate temperature change available.
Such errors can readily occur, especially when one considers that thermal cold packs are often employed in emergency situations. Also with regard to the pack of U.S. Pat. No. 4,462,224, it should be pointed out that considerable effort must be expended by the user to produce the desired results. A great deal of manual manipulation must take place in order to bring the interiors of the compartments into communication in the proper manner as well as to mix same.
It should also be mentioned that the three compartment configuration employed in the device of U.S. Pat. No. 4,462,224 results in much of the overall surface area, e.g. one third, of the pack being rendered useless or non-operative when used as an instant hot or cold pack. That is, only the surface area corresponding to the first and second compartments may be usefully applied to an object during the instant pack phase. The remaining third compartment, which is not mixed until the cold has essentially disappeared, is cumbersome and likely to get in the way when the pack is being utilized in its instant mode.
Mixing of the contents of the third compartment with the previously mixed ingredients of the first and second compartments is also a time consuming and tedious process. The user must employ both hands to knead the material in the third compartment with the materials in the first and second compartments. Considerable time and energy must be expended to provide for a thorough mix.